Many of the present day automotive vehicles having automatic transmissions use electronically controlled mechanisms to establish the operating condition of the transmission. These control systems typically include solenoids, switches, and electronic circuitry.
For reasons of safety and government regulation, it is required that these automatic transmissions incorporate transmission shift-lock capability wherein the transmission shift lever and the ignition switch have limited movement unless certain conditions are met. In accordance with the shift-lock function, when starting the vehicle, the transmission shift lever can be moved out of the park position only if the driver presses on the brake pedal and if the ignition key is turned so as to be in the run position. Various systems have been proposed and utilized to achieve a combined brake shift interlock and ignition switch interlock function wherein a solenoid is engaged to prevent movement of the transmission shift lever. Most of these prior art systems have proved to function as intended but at the expense of introducing unwanted noise into the brake shift interlock system which can be heard by a vehicle's operator. The noise created typically originates from a couple of sources. Specifically, a source of noise is the vibration of the engine which causes the plunger within the solenoid housing to vibrate. A second source of noise results from the sudden movement of the solenoid, which causes the solenoid to contact the end stops when energized and de-energized.
It would be desirable, therefore, to provide a brake shift interlock system, which reduce the noise created by plunger vibration and noise created by contact with the end stops in addition to meeting governmental and vehicle manufacturer system requirements.